/*
 * efone - Distributed internet phone system.
 *
 * (c) 1999,2000 Krzysztof Dabrowski
 * (c) 1999,2000 ElysiuM deeZine
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 */

/* based on implementation by Finn Yannick Jacobs */

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include "crc32.h"

/* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
 * so make sure, you call it before using the other functions!
 */
uint32_t crc_tab[256];

/* chksum_crc() -- to a given block, this one calculates the crc32-checksum until the length is
 * reached. the crc32-checksum will be the result.
 */
uint32_t chksum_crc32 (unsigned char *block, unsigned int length)
{
    unsigned long crc;
    unsigned long i;

    crc = 0xFFFFFFFF;
    for (i = 0; i < length; i++) {
        crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
    }
    return (crc ^ 0xFFFFFFFF);
}

/* chksum_crc32gentab() -- to a global crc_tab[256], this one will
 * calculate the crcTable for crc32-checksums. it is generated to the polynom [..]
 */
void chksum_crc32gentab ()
{
    unsigned long crc, poly;
    int i, j;

    poly = 0xEDB88320L;
    for (i = 0; i < 256; i++) {
        crc = i;
        for (j = 8; j > 0; j--) {
            if (crc & 1) {
                crc = (crc >> 1) ^ poly;
            } else {
                crc >>= 1;
            }
        }
        crc_tab[i] = crc;
    }
}
